So. You’ve just received a shiny new MBP, then a few weeks later Apple go and release an update. And the couple of thousand you just laid out suddenly doesn’t seem as worthwhile as it did the month before when it arrived.
Anyway help is here: there is a site for that. As Apple normally releases new models at regular intervals Apple Store Check counts down the days between the release cycles and tells you whether or not it is safe to buy a Mac.
Thanks to @danbenjamin for the helpful point in this direction.